This invention relates to ultrasonic temperature measurement.
The invention has arisen in consideration of the severe problems that arise in measuring temperature of coolant flowing in a fast-fission nuclear reactor cooled by liquid sodium. Monitoring of coolant temperature is not only vital for normal control purposes but it is also vital for safety purposes as temperature trends and transients can foreshadow the onset of incidents like blockage of coolant flow which might cause solid nuclear fuel to melt if corrective or preventative action is not taken. Various solutions to these problems have been considered such as reliance on flowmeter or thermocouple readings or by the acoustic detection of coolant boiling. However, with these known solutions uncertainties may arise especially where the normal flow is low, or there is cross-flow in which a normal flow could mask an abnormal flow. These uncertainties are increased when, as is often the case, the flow or temperature measuring device cannot be located precisely at the most sensitive localities (which are usually the discharge points of flow from defined channels into bulk zones) because of access or obstruction problems.
Whilst, current practice does not itself involve any hazards, as the acceptable margin of safety can be suitably achieved, improved standard is continuously being sought. The present invention provides such an improved standard by the use of ultrasonics which may either replace or work in harness with known systems.
The use of ultrasonic techniques to measure temperature is well known--see, for example, British Patent Specifications Nos. 2114299, 2002118, 1300159, 1202182, 1178529, 1178385 and 1035763. Patent No. 1300159, for instance, is specifically concerned with a device for ultrasonic measurement of the temperature of liquid metal coolant within a nuclear reactor. Such a device suffers from the drawback that it is invasive in the sense that the hardware is physically located at the position at which the temperature measurement is to be made and therefore interferes with the flow conditions prevailing at that position.